U.S. patent application number 14/883051 was filed with the patent office on 2017-04-20 for large scale optical switch using asymmetric 1x2 elements.
The applicant listed for this patent is NISTICA, INC.. Invention is credited to JEFFERSON L. WAGENER.
Application Number | 20170108651 14/883051 |
Document ID | / |
Family ID | 58518529 |
Filed Date | 2017-04-20 |
United States Patent
Application |
20170108651 |
Kind Code |
A1 |
WAGENER; JEFFERSON L. |
April 20, 2017 |
Large Scale Optical Switch using Asymmetric 1x2 Elements
Abstract
An optical switching arrangement includes a plurality of input
and output waveguides. Each of the input waveguides has a first
plurality of 1.times.2 optical switches associated therewith and
extending therealong. Each of the output waveguides has a second
plurality of 1.times.2 optical switches associated therewith and
extending therealong. Each of the first and second plurality of
optical switches is selectively switchable between a through-state
and a cross-state. The input and output waveguides are arranged
such that optical losses arising for any wavelength of light only
depend on a length of segments of the input and output waveguides
located between adjacent ones of the 1.times.2 optical switches.
Each of the first plurality of optical switches associated with
each of the input waveguides is optically coupled to one of the
second plurality of optical switches in a different one of the
output waveguides when both optical switches are in the
cross-state.
Inventors: |
WAGENER; JEFFERSON L.;
(MORRISTOWN, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISTICA, INC. |
BRIDGEWATER |
NJ |
US |
|
|
Family ID: |
58518529 |
Appl. No.: |
14/883051 |
Filed: |
October 14, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 2006/12145
20130101; G02B 6/283 20130101; G02B 6/3596 20130101; G02B 6/032
20130101; G02B 6/3592 20130101; G02B 6/3556 20130101; G02B 6/359
20130101; G02B 6/3546 20130101; G02B 6/3508 20130101; G02B 6/356
20130101; G02B 6/3504 20130101; G02B 6/3584 20130101 |
International
Class: |
G02B 6/35 20060101
G02B006/35; G02B 6/032 20060101 G02B006/032 |
Claims
1. An optical switching arrangement, comprising: a plurality of
input waveguides, each of the input waveguides having a first
plurality of 1.times.2 optical switches associated therewith and
extending therealong; a plurality of output waveguides, each of the
output waveguides having a second plurality of 1.times.2 optical
switches associated therewith and extending therealong; each of the
optical switches in the first and second plurality of optical
switches being selectively switchable between first and second
states such that in a first state each optical switch allows light
propagating in the input or output waveguide with which it is
associated to continue propagating therethrough undisturbed without
encountering any intervening mode perturbing structures between
adjacent ones of the 1.times.2 switches and in a second state each
optical switch couples light into or out of the input or output
waveguide with which it is associated; and wherein each of the
first plurality of optical switches associated with each of the
input waveguides is optically coupled to one of the second
plurality of optical switches in a different one of the output
waveguides when both optical switches are in the second state.
2. The optical switching arrangement of claim 1 wherein each of the
1.times.2 switches comprises: a displaceable optical cross-guide,
the 1.times.2 switch being in the first state when the optical
cross-guide is a first distance from the input or output waveguide
with which each of the 1.times.2 switches is respectively
associated and in a second state when the optical cross-guide is a
second distance from the input or output waveguide with which each
of the 1.times.2 switches is respectively associated; an actuator
for selectively displacing the displaceable optical cross-guide so
that its distance from the input or output waveguide with which it
is associated is equal to the first or second distance.
3. The optical switching arrangement of claim 2 wherein the
actuator is a MEMs-based actuator.
4. The optical switching arrangement of claim 2 wherein the
actuator is a digital, two-state actuator.
5. The optical switching arrangement of claim 2 wherein the
actuator is latching in the first state.
6. The optical switching arrangement of claim 1 further comprising
a plurality of optical coupling elements each optically coupling
one of the first plurality of optical switches associated with each
of the input waveguides to one of the second plurality of optical
switches associated with one of the output waveguides when both
optical switches are in the second state.
7. The optical switching arrangement of claim 1 further comprising
a first planar lightwave or photonic integrated circuit in which
the plurality of input waveguides and the first plurality of
1.times.2 optical switches are integrated.
8. The optical switching arrangement of claim 7 further comprising
a second planar lightwave or photonic integrated circuit in which
the plurality of output waveguides and the second plurality of
1.times.2 optical switches are integrated.
9. The optical switching arrangement of claim 8 wherein the first
and second planar lightwave or photonic integrated circuits are
stacked on top of one another.
10. The optical switching arrangement of claim 9 wherein the first
and second planar lightwave or photonic integrated circuits are
hybridly attached to one another.
11. The optical switching arrangement of claim 9 wherein the first
and second lightwave or photonic integrated circuits are
monolithically integrated with one another.
12. The optical switching arrangement of claim 9 further comprising
a plurality of vertical couplers each optically coupling one of the
first plurality of optical switches associated with each of the
input waveguides to one of the second plurality of optical switches
associated with one of the output waveguides when both optical
switches are in the second state.
13. The optical switching arrangement of claim 1 wherein each of
the 1.times.2 optical switches in the first and second pluralities
of 1.times.2 optical switches exhibit lower loss in the first state
than in the second state
14. The optical switching arrangement of claim 1 further comprising
a controller for selectively switching light from any one of the
input waveguides to any one of the output waveguides by causing one
of the first plurality of optical switches and one of the second
plurality of optical switches to be placed in the second state and
causing all remaining optical switches in the first and second
pluralities of optical switches to be placed in the first
state.
15. The optical switching arrangement of claim 1 further comprising
a controller for (i) selectively switching light from a first
selected one of the input waveguides to a first selected one of the
output waveguides by causing one of the first plurality of optical
switches and one of the second plurality of optical switches to be
placed in the second state and (ii) simultaneously switching light
from a second selected one of the input waveguides to a second
selected one of the output waveguides by causing another of the
first plurality of optical switches and another of the second
plurality of optical switches to be placed in the second state
while (iii) causing all remaining optical switches in the first and
second pluralities of optical switches to be placed in the first
state.
16. The optical switching arrangement of claim 1 wherein the input
and output waveguides are air clad waveguides.
17. The optical switching arrangement of claim 1 wherein the input
and output waveguides are single mode waveguides.
18. The optical switching arrangement of claim 1 wherein the
plurality of input and output waveguides support light traveling in
a single polarization state.
19. The optical switching arrangement of claim 18 further
comprising: a second plurality of input waveguides, each of the
input waveguides in the second plurality having a third plurality
of 1.times.2 optical switches associated therewith and extending
therealong; a second plurality of output waveguides, each of the
output waveguides in the second plurality having a fourth plurality
of 1.times.2 optical switches associated therewith and extending
therealong; each of the optical switches in the third and fourth
plurality of optical switches being selectively switchable between
first and second states such that in a first state each optical
switch allows light propagating in the input or output waveguide
with which it is associated to continue propagating therethrough
undisturbed without encountering any intervening mode perturbing
structures between adjacent ones of the 1.times.2 switches and in a
second state of the optical switches couples light into or out of
the input or output waveguide with which it is associated; wherein
each of the third plurality of optical switches associated with
each of the input waveguides in the second plurality is optically
coupled to one of the fourth plurality of optical switches in a
different one of the output waveguides in the second plurality when
both optical switches in the third and fourth pluralities are in
the second state; and a plurality of polarization splitters each
coupling an input port of one of the plurality of input waveguides
to an input port of one of the second plurality of input
waveguides.
20. The optical switching arrangement of claim 19 further
comprising a polarization rotator for rotating the polarization of
light in the second plurality of input waveguides into a common
polarization state with light in the plurality of input
waveguides.
21. The optical switching arrangement of claim 19 further
comprising a first planar lightwave circuit in which are integrated
the plurality of input waveguides, the first plurality of 1.times.2
optical switches, the second plurality of input waveguides and the
third plurality of 1.times.2 optical switches.
22. The optical switching arrangement of claim 21 wherein the
plurality of input waveguides and the second plurality of input
waveguides are parallel to one another.
23. The optical switching arrangement of claim 22 wherein the input
waveguides in each pair of input waveguides that are coupled by one
of the polarization splitters are adjacent to one another.
24. The optical switching arrangement of claim 1 further
comprising: a photodetector; at least one additional 1.times.2
optical switch being associated with and extending along at least
one of the input waveguides and/or the output waveguides such that
light is coupled from the at least one input and/ or output
waveguide to the photodetector when the additional 1.times.2 switch
is in the second state.
25. An optical switching arrangement, comprising: a plurality of
input waveguides, each of the input waveguides having a first
plurality of 1.times.2 optical switches associated therewith and
extending therealong; a plurality of output waveguides, each of the
output waveguides having a second plurality of 1.times.2 optical
switches associated therewith and extending therealong, each of the
first and second plurality of optical switches being selectively
switchable between a through-state and a cross-state, the input and
output waveguides being arranged such that light propagating in any
and all of the input and output waveguides does not traverse a
waveguide crossing; wherein each of the first plurality of optical
switches associated with each of the input waveguides is optically
coupled to one of the second plurality of optical switches in a
different one of the output waveguides when both optical switches
are in the cross-state.
26. An optical switching arrangement, comprising: a plurality of
input waveguides, each of the input waveguides having a first
plurality of 1.times.2 optical switches associated therewith and
extending therealong; a plurality of output waveguides, each of the
output waveguides having a second plurality of 1.times.2 optical
switches associated therewith and extending therealong, each of the
first and second plurality of optical switches being selectively
switchable between a through-state and a cross-state, the input and
output waveguides being arranged such that optical losses arising
for any wavelength of light only depend on a length of segments of
the input and output waveguides located between adjacent ones of
the 1.times.2 optical switches; wherein each of the first plurality
of optical switches associated with each of the input waveguides is
optically coupled to one of the second plurality of optical
switches in a different one of the output waveguides when both
optical switches are in the cross-state.
27. An optical switching arrangement, comprising: a plurality of
input waveguides, each of the input waveguides having a first
plurality of 1.times.2 optical switches associated therewith and
extending therealong; a plurality of output waveguides, each of the
output waveguides having a second plurality of 1.times.2 optical
switches associated therewith and extending therealong; each of the
optical switches in the first and second plurality of optical
switches being selectively switchable between first and second
states such that in a first state each optical switch allows light
propagating in the input or output waveguide with which it is
associated to continue propagating therethrough and in a second
state each optical switch couples light into or out of the input or
output waveguide with which it is associated, the input and output
waveguides being arranged such that optical losses arising for any
wavelength of light only depend on a length of segments of the
input and output waveguides located between adjacent ones of the
1.times.2 optical switches; and wherein each of the first plurality
of optical switches associated with each of the input waveguides is
optically coupled to one of the second plurality of optical
switches in a different one of the output waveguides when both
optical switches are in the second state, each of the 1.times.2
switches including (i) a displaceable optical cross-guide, the
1.times.2 switch being in the first state when the optical
cross-guide is a first distance from the input or output waveguide
with which each of the 1.times.2 switches is respectively
associated and in a second state when the optical cross-guide is a
second distance from the input or output waveguide with which each
of the 1.times.2 switches is respectively associated and (ii) an
actuator for selectively displacing the displaceable optical
cross-guide so that its distance from the input or output waveguide
with which it is associated is equal to the first or second
distance.
28. The optical switching arrangement of claim 26 wherein each of
the 1.times.2 switches comprises: a displaceable optical
cross-guide, the 1.times.2 switch being in the through state when
the optical cross-guide is a first distance from the input or
output waveguide with which each of the 1.times.2 switches is
respectively associated and in the cross-state when the optical
cross-guide is a second distance from the input or output waveguide
with which each of the 1.times.2 switches is respectively
associated; an actuator for selectively displacing the displaceable
optical cross-guide so that its distance from the input or output
waveguide with which it is associated is equal to the first or
second distance.
29. The optical switching arrangement of claim 28 wherein the
actuator is a MEMs-based actuator.
30. The optical switching arrangement of claim 28 wherein the
actuator is a digital, two-state actuator.
31. The optical switching arrangement of claim 28 wherein the
actuator is latching in the through-state.
32. The optical switching arrangement of claim 26 further
comprising a plurality of optical coupling elements each optically
coupling one of the first plurality of optical switches associated
with each of the input waveguides to one of the second plurality of
optical switches associated with one of the output waveguides when
both optical switches are in the cross-state.
33. The optical switching arrangement of claim 26 further
comprising a first planar lightwave or photonic integrated circuit
in which the plurality of input waveguides and the first plurality
of 1.times.2 optical switches are integrated.
34. The optical switching arrangement of claim 33 further
comprising a second planar lightwave or photonic integrated circuit
in which the plurality of output waveguides and the second
plurality of 1.times.2 optical switches are integrated.
35. The optical switching arrangement of claim 34 wherein the first
and second planar lightwave or photonic integrated circuits are
stacked on top of one another.
36. The optical switching arrangement of claim 35 wherein the first
and second planar lightwave or photonic integrated circuits are
hybridly attached to one another.
37. The optical switching arrangement of claim 35 wherein the first
and second lightwave or photonic integrated circuits are
monolithically integrated with one another.
38. The optical switching arrangement of claim 35 further
comprising a plurality of vertical couplers each optically coupling
one of the first plurality of optical switches associated with each
of the input waveguides to one of the second plurality of optical
switches associated with one of the output waveguides when both
optical switches are in the cross-state.
39. The optical switching arrangement of claim 26 wherein each of
the 1.times.2 optical switches in the first and second pluralities
of 1.times.2 optical switches exhibit lower loss in the
through-state than in the cross-state
40. The optical switching arrangement of claim 26 further
comprising a controller for selectively switching light from any
one of the input waveguides to any one of the output waveguides by
causing one of the first plurality of optical switches and one of
the second plurality of optical switches to be placed in the
cross-state and causing all remaining optical switches in the first
and second pluralities of optical switches to be placed in the
through-state.
41. The optical switching arrangement of claim 26 further
comprising a controller for (i) selectively switching light from a
first selected one of the input waveguides to a first selected one
of the output waveguides by causing one of the first plurality of
optical switches and one of the second plurality of optical
switches to be placed in the cross-state and (ii) simultaneously
switching light from a second selected one of the input waveguides
to a second selected one of the output waveguides by causing
another of the first plurality of optical switches and another of
the second plurality of optical switches to be placed in the
cross-state while (iii) causing all remaining optical switches in
the first and second pluralities of optical switches to be placed
in the through-state.
42. The optical switching arrangement of claim 26 wherein the input
and output waveguides are air clad waveguides.
43. The optical switching arrangement of claim 26 wherein the input
and output waveguides are single mode waveguides.
44. The optical switching arrangement of claim 26 wherein the
plurality of input and output waveguides support light traveling in
a single polarization state.
45. The optical switching arrangement of claim 44 further
comprising: a second plurality of input waveguides, each of the
input waveguides in the second plurality having a third plurality
of 1.times.2 optical switches associated therewith and extending
therealong; a second plurality of output waveguides, each of the
output waveguides in the second plurality having a fourth plurality
of 1.times.2 optical switches associated therewith and extending
therealong; each of the optical switches in the third and fourth
plurality of optical switches being selectively switchable between
through and cross-states such that in a through state each optical
switch allows light propagating in the input or output waveguide
with which it is associated to continue propagating therethrough
undisturbed without encountering any intervening mode perturbing
structures between adjacent ones of the 1.times.2 switches and in a
cross-state of the optical switches couples light into or out of
the input or output waveguide with which it is associated; wherein
each of the third plurality of optical switches associated with
each of the input waveguides in the second plurality is optically
coupled to one of the fourth plurality of optical switches in a
different one of the output waveguides in the second plurality when
both optical switches in the third and fourth pluralities are in
the cross-state; and a plurality of polarization splitters each
coupling an input port of one of the plurality of input waveguides
to an input port of one of the second plurality of input
waveguides.
46. The optical switching arrangement of claim 45 further
comprising a polarization rotator for rotating the polarization of
light in the second plurality of input waveguides into a common
polarization state with light in the plurality of input
waveguides.
47. The optical switching arrangement of claim 45 further
comprising a first planar lightwave circuit in which are integrated
the plurality of input waveguides, the first plurality of 1.times.2
optical switches, the second plurality of input waveguides and the
third plurality of 1.times.2 optical switches.
48. The optical switching arrangement of claim 47 wherein the
plurality of input waveguides and the second plurality of input
waveguides are parallel to one another.
49. The optical switching arrangement of claim 48 wherein the input
waveguides in each pair of input waveguides that are coupled by one
of the polarization splitters are adjacent to one another.
50. The optical switching arrangement of claim 26 further
comprising: a photodetector; at least one additional 1.times.2
optical switch being associated with and extending along at least
one of the input waveguides and/or the output waveguides such that
light is coupled from the at least one input and/ or output
waveguide to the photodetector when the additional 1.times.2 switch
is in the cross-state.
Description
BACKGROUND
[0001] There is a need in the industry for large port count optical
switches. These switches are typically designed to be single mode
with broad optical bandwidth and a multitude of input and output
fibers. Multiple practical techniques exist for making smaller port
count switches (e.g., 2.times.2, 4.times.4, 8.times.8, 16.times.16)
but most of these techniques do not scale well at or above
32.times.32. Specifically, performance parameters of interest start
become more difficult to achieve, including but not limited to
loss, crosstalk and switching speed. Switches are needed that have
128.times.128 ports or higher with low loss and switching speeds
significantly faster than current generation switches.
[0002] Most high port count (e.g., greater than 128) switches use a
3D MEMs architecture, where a 2 axis tilt mirror is used to steer a
free space beam from one input port to a second mirror that then
steers the beam to a second output port. Due to the inherent modal
propagation in free space, these switches are difficult to scale
without sacrificing switching time. This is fundamentally due to
the larger beam requirements and therefore larger mirrors as the
port count grows.
SUMMARY
[0003] In accordance with one aspect of the subject matter
described herein, an optical switching arrangement includes a
plurality of input waveguides and a plurality of output waveguides.
Each of the input waveguides has a first plurality of 1.times.2
optical switches associated therewith and extending therealong.
Each of the output waveguides has a second plurality of 1.times.2
optical switches associated therewith and extending therealong.
Each of the optical switches in the first and second plurality of
optical switches are selectively switchable between first and
second states such that in a first state each optical switch allows
light propagating in the input or output waveguide with which it is
associated to continue propagating therethrough undisturbed without
encountering any intervening mode perturbing structures between
adjacent ones of the 1.times.2 switches and in a second state each
optical switch couples light into or out of the input or output
waveguide with which it is associated. Each of the first plurality
of optical switches associated with each of the input waveguides is
optically coupled to one of the second plurality of optical
switches in a different one of the output waveguides when both
optical switches are in the second state.
[0004] In one particular implementation, each of the 1.times.2
switches includes a displaceable optical cross-guide. The 1.times.2
switch is in the first state when the optical cross-guide is a
first distance from the input or output waveguide with which each
of the 1.times.2 switches is respectively associated and in a
second state when the optical cross-guide is a second distance from
the input or output waveguide with which each of the 1.times.2
switches is respectively associated. An actuator selectively
displaces the displaceable optical cross-guide so that its distance
from the input or output waveguide with which it is associated is
equal to the first or second distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1A shows an input platform for an M.times.M optical
switch and FIG. 1B shows an output platform for an M.times.M
optical switch.
[0006] FIG. 2 shows a plan view of a single input or output
waveguide of the type shown on the input and output platforms shown
in FIGS. 1A and 1B.
[0007] FIGS. 3A and 3B are cross-sectional views of an asymmetric
1.times.2 switch.
[0008] FIG. 4 shows an input platform for an M.times.M optical
switch that supports polarization diversity.
DETAILED DESCRIPTION
[0009] As detailed below, an M.times.M optical switch is provided
which includes an array of input optical waveguides and an array of
output optical waveguides that may each be located on a separate
platform. A series of asymmetric 1.times.2 optical switches are
integrated with each input waveguide. Each asymmetric 1.times.2
switch associated with any given waveguide is able to switch light
propagating in that waveguide to a different one of the output
waveguides. In this way an optical input signal received by an
input waveguide can be selectively directed to any output
waveguide.
[0010] FIG. 1A shows an input platform for an M.times.M optical
switch. The input platform includes an array of input optical
waveguides 110.sub.1, 110.sub.2, 110.sub.3 . . . 110.sub.8
(collectively "110") that may be formed on a common substrate 105.
As shown, in some embodiments the waveguides 110 may be parallel to
one another, although this need not be the case in all embodiments.
Although 8 input optical waveguides 110 are shown in this example,
any number of input optical waveguides may be employed, with each
input waveguide corresponding to one input port of an optical
switch. Accordingly, for a large scale optical switch having, for
instance, 128 input and output ports, there will be 128 input
optical waveguides 110. Thus, more generally, for an M.times.M
optical switch there will be M input optical waveguides 110.
[0011] A series of 1.times.2 asymmetric optical switches 120 are
located along each of the waveguides 110. Specifically, for an
M.times.M optical switch, there will be M 1.times.2 asymmetric
switches 120 located along each waveguide 110. As shown in FIG. 1A
for an 8.times.8 optical switch, 1.times.2 switches 120.sub.11,
120.sub.12, 120.sub.13 . . . 120.sub.18 are located along waveguide
110.sub.1, 1.times.2 switches 120.sub.21, 120.sub.22, 120.sub.23 .
. . 120.sub.28 are located along waveguide 110.sub.2, and so on. As
explained below, the 1.times.2 asymmetric switches 120 are
asymmetric in the sense that they exhibit low loss when in a first
state and may exhibit significantly higher loss when in a second
state. A vertical coupler 130 is associated with each 1.times.2
asymmetric switch 120. As also explained below, when a 1.times.2
switch is in its open or on state, light received by the 1.times.2
switch will be directed to the vertical coupler 130 with which it
is associated. The vertical coupler 130 will, in turn, pass the
light to another 1.times.2 switch located on an output waveguide
platform, which is discussed below.
[0012] Each 1.times.2 switch 120 can direct light propagating in
the input waveguide 110 with which it is associated in one of two
directions based on the state of the asymmetric switch 120. In a
first state, referred to as the through-state, the 1.times.2 switch
causes the light to continue propagating in the input waveguide
110. That is, the light continues along the thru-path largely
unperturbed. In a second state, referred to as a cross state, the
1.times.2 switch 120 couples the light out of the input waveguide
110 and directs it to the vertical coupler 130 associated with that
asymmetric 1.times.2 switch 120.
[0013] The 1.times.2 asymmetric switches 120 are designed to have
very low loss in the first or through-state Accordingly, if all the
asymmetric 1.times.2 switches associated with a given input
waveguide 110 are in the through-state, then the light propagating
in that waveguide will pass through that waveguide largely
unperturbed. For example, in some embodiments, the 1.times.2
asymmetric switches 120 may have a loss in the through-state of
about 0.0001 db. As explained below, a much greater amount of loss
may be tolerated when the 1.times.2 switch is in the second or
cross state.
[0014] FIG. 1B shows an output platform for the aforementioned
8.times.8 optical switch. The output platform includes an array of
output optical waveguides 210.sub.1, 210.sub.2, 210.sub.3 . . .
210.sub.8 (collectively "210") that may be formed on a common
substrate 205. In general, the array of output optical waveguides
210 is largely the same as the array of input optical waveguides
110, with the same number of waveguides and the same number of
1.times.2 asymmetric optical switches. That is, similar to the
input waveguide platform in FIG. 1A, the output waveguide platform
of FIG. 1B includes a series of 1.times.2 asymmetric optical
switches 220 that are located along each of the waveguides 110.
Specifically, for an M.times.M optical switch, there will be M
1.times.2 asymmetric switches 220 located along each waveguide 210.
As shown in FIG. 1B, 1.times.2 switches 220.sub.11, 220.sub.12,
220.sub.13 . . . 220.sub.18 are located along waveguide 210.sub.1,
1.times.2 switches 220.sub.21, 220.sub.22, 220.sub.23 . . .
220.sub.28 are located along waveguide 210.sub.2, and so on. The
asymmetric optical switches 220 are similar to the asymmetric
optical switches 110 described above. One of the vertical couplers
130 associated with each 1.times.2 asymmetric switch 120 is also
associated with one of the 1.times.2 asymmetric switches 220.
[0015] In one embodiment, input and output waveguide platforms are
stacked or overlaid on top of one another so that corresponding
asymmetric 1.times.2 switches 120 and 220 (i.e., pairs of switches
120 and 220 that are optically coupled to one another vis a common
vertical coupler 130) are aligned with one another. That is, input
and output waveguide platforms are located in different planes with
asymmetric 1.times.2 switch 120.sub.ij being located above (or
below) asymmetric switch 220.sub.ji. Thus, for example, asymmetric
1.times.2 switch 120.sub.12 is located above (or below) asymmetric
1.times.2 switch 220.sub.21 and are optically coupled to one
another by vertical coupler 130.sub.12. As another example,
asymmetric 1.times.2 switch 120.sub.32 is located above (or below)
asymmetric 1.times.2 switch 220.sub.23 and are optically coupled to
one another by vertical coupler 130.sub.32. For simplicity of
manufacturing, each 1.times.2 switch in pairs of corresponding
switches 120 and 220 may be located directly above or below one
another, although this need not necessarily be the case.
[0016] As shown in FIGS. 1A and 1B, each of the 1.times.2 optical
switches is selectively addressable by a controller 150 for placing
the switches in the through-state or the cross-state. In operation,
an optical signal propagating through one of the input waveguides
110 can be selectively switched to one of the output waveguides by
placing both corresponding asymmetric 1.times.2 switches 120.sub.ij
and 220.sub.ji in the cross-state. Thus, for example, by placing
both asymmetric 1.times.2 switch 120.sub.12 and asymmetric
1.times.2 switch 220.sub.21 in the cross-state, an optical signal
can be switched from input waveguide 110.sub.1 to output waveguide
220.sub.2 via vertical coupler 130.sub.12. As another example, by
placing both symmetric 1.times.2 switch 120.sub.32 and asymmetric
1.times.2 switch 220.sub.23 in the cross-state, an optical signal
can be switched from input waveguide 1103 to output waveguide
220.sub.2 via vertical coupler 130.sub.23. Thus, in this way, by
placing both asymmetric 1.times.2 switches in the appropriately
chosen pair of corresponding asymmetric 1.times.2 switches in the
cross-state an optical signal can be switched from any input
waveguide 110 to any output waveguide 220.
[0017] It should be noted that the arrangement of input and output
waveguides shown in FIGS. 1A and 1B is by way of example only. More
generally, the input and output waveguides may be arranged in any
manner that allows corresponding pairs of 1.times.2 switches placed
in the cross-state to couple an optical signal from any input
waveguide 110 to any output waveguide 220 while the optical signal
only traverses other 1.times.2 switches in the through-state.
[0018] As illustrated above, an optical signal can be switched from
any input waveguide 110 to any output waveguide 220 by placing only
a single asymmetric 1.times.2 switch in each waveguide in the
cross-state. At the same time all the other asymmetric 1.times.2
switches in each waveguide are in the through-state. Thus, an
optical signal will generally traverse multiple asymmetric
1.times.2 switches in the through-state and only a single pair of
asymmetric 1.times.2 switches in the cross-state. As a consequence,
it is important that the asymmetric 1.times.2 switch exhibit low
loss in the through-state. On the other hand, since the optical
signal only traverses a single pair of asymmetric 1.times.2
switches in the cross-state, a significantly greater amount of loss
can be tolerated when the asymmetric 1.times.2 switches are in the
cross-state.
[0019] The asymmetric 1.times.2 switches 130 employed in optical
switch 100 may be based on any suitable technology. For instance,
in one embodiment, a mechanically-actuated type switch switch may
be employed, one example of which will be described with reference
to FIGS. 3 and 4. This particular example will be illustrated using
a micro-electromechanical (MEMs) device as the actuator.
[0020] FIG. 2 shows a plan view of a single input or output
waveguide 310 of the type shown in FIGS. 1A and 1B as waveguides
110 and 210, respectively. The waveguide 310 serves as the
stationary through-guide portion of the asymmetric 1.times.2 switch
300. A second waveguide 320 serves as the actuatable cross-guide of
the asymmetric 1.times.2 switch 300, which is movable between a
first or "on" position 340 and a second or "off" position 350. When
the cross-guide 320 is in the on-position 340 it is sufficiently
close to the through guide 310 to couple light from the through
guide to the cross-guide 320. Likewise, when the cross-guide 320 is
in the off-position 350 it is sufficiently remote from the through
guide 310 to cause no measureable mode perturbation in the through
guide 310. As a consequence light is not coupled to any substantial
degree between the cross-guide 320 and the through guide 310 while
in the off-position 350. That is, when the cross-guide 310 is in
the on-position 340 the asymmetric 1.times.2 switch 300 is in the
cross-state and when the cross-guide 310 is in the off-position 350
the asymmetric 1.times.2 switch 300 is in the through-state.
[0021] One or more stoppers 345 may be placed between the
through-guide 310 and the cross-guide 320 so that the cross-guide
320 lands on the stopper 345 when transitioning to the on position
340. In this way a consistent gap may be maintained between the
through-guide 310 and the cross-guide 320 when the cross-guide 320
is in the on position 340. In one embodiment the stopper 345 is
secured to the cross-guide 320.
[0022] FIGS. 3A and 3B are cross-sectional views of the asymmetric
1.times.2 switch 300 of FIG. 3 taken along line A-A'. As shown,
though-guide 310 extends on a support 405, which in turn is located
on a platform 412 (e.g., substrates 105 or 205 in FIGS. 1A or 1B).
The visible, proximate end of cross-guide 320 is suspended in space
while the distal end of the cross-guide 320 is secured to a second
support (not shown) that is located on the platform 412. A
laterally displaceable actuator 415 is located on a support 407,
which in turn is located on the platform 412. Laterally
displaceable actuator 415 is adjacent to the proximate end of the
cross-guide 320 and is movable in a first direction (the left
direction in FIGS. 3A and 3B) so that it exerts a lateral force on
the cross-guide 320, which undergoes a displacement to the on
position 340, as shown in FIG. 3A. When the laterally displaceable
actuator 415 is retracted, the cross-guide 320 returns to the
position shown in FIG. 3B, which corresponds to the off-position
350 of the cross-guide 320.
[0023] As previously mentioned, in one embodiment the laterally
displaceable actuator 415 is a MEMs-based actuator. In one
particular embodiment the MEMs-based actuator may be a digital
two-state device, with one state corresponding to the on-position
340 of the cross-guide 320 and the other state corresponding to the
off-position 350 of the cross-guide 320. The MEMs-based actuator
415 may also be latching, with the off-positon of FIG. 3(b) being
the latched state in which the actuator 415 is normally maintained.
In this way a failure in one of the asymmetric 1.times.2 switches
will not cause a complete failure of the entire M.times.M optical
switch 300. Rather, the M.times.M optical switch 300 will simply
lose the capability of switching between one particular input and
output waveguide but would otherwise remain operational. Of course,
in other embodiments the actuator 415 may be latched so that the
cross-guide 210 is in the on-position or, alternatively, the
actuator 415 may be unlatched.
[0024] When in the off-position, the distance between the
cross-guide 320 and through-guide 310 should be sufficiently great
so that no measurable optical mode perturbations are caused in the
through-guide 310. Thus, the distance traveled in the lateral
direction by the actuator 415 when transitioning from the
off-position 350 to the on-position 340 generally should be large
compared to the mode field radius (e.g., several mode field
diameters). By way of example, in one embodiment, for a waveguide
having a 1 micron core with a mode radius of about 1 microns, the
distance traveled in the lateral direction by the actuator 415 when
transitioning from the off-position to the on-position may be about
3-5 microns. Likewise, in some embodiments the overall dimensions
of the individual 1.times.2 switches are on the order of about 50
microns or less.
[0025] Of course, instead of being a MEMs-based switch, the
1.times.2 optical switches may employ other technologies. For
instance, in one embodiment the 1.times.2 optical switches may be
acousto-optical switches.
[0026] The vertical couplers 130 shown in FIGS. 1A and 1B may be
any suitable type of vertical coupler such as a vertical adiabatic
coupler for out-of-plane optical coupling between different
waveguides. In one particular example, the vertical couplers 130
may be grating-based vertical couplers in which a grating is etched
into a waveguide. The grating at least partially diffracts light
traveling in the waveguide so that the light is coupled out of the
plane of the waveguide at some angle of diffraction and coupled
into another waveguide.
[0027] In some embodiments of the invention the input and output
platforms of the optical switch may be formed from one or more
Planar Lightwave Circuits (PLCs). PLCs are optical systems
comprising one or more single or multi-mode waveguides that are
integrated on the surface of a semiconductor substrate, where the
waveguides are typically combined with other optical components
(such as the 1.times.2 switches and the vertical adiabatic couplers
described herein, for example) to provide complex optical
functionality. More specifically, the waveguides are usually
embedded within an optical layer that may consist of buffer layers,
cladding layers, core layers and encapsulation layers formed on the
planar substrate which is frequently formed from doped/undoped
silicon, LiNbO.sub.3, InP, GaAs, and/or polymer (including
thermo-optic and electro-optic polymers). The substrate may serve
as a mechanical support for the otherwise fragile waveguide and it
can, if desired, also play the role of the bottom portion of the
cladding. In addition, it can serve as a portion of the fixture to
which optical fibers are attached so as to optically couple cores
of an input/output fibers to the cores of the waveguide.
[0028] Fabrication techniques required for manufacturing planar
lightwave circuits using silicon are generally well known. For
instance, planar lightwave circuits may be fabricated using
standard semiconductor manufacturing techniques. Therefore, the
fabrication of the planar lightwave circuit can be accomplished
using standard monolithic semiconductor manufacturing techniques
including chemical vapor phase deposition techniques, physical
vapor deposition or sputtering techniques, evaporation techniques,
spin-on deposition techniques, photolithography, wet or dry etching
techniques, etc. The specific fabrication technique is often chosen
with respect to manufacturing equipment and materials used in the
deposition. As such, the switches disclosed herein may be
fabricated in conjunction with many techniques and materials, as
will be recognized by one of ordinary skill in the art.
[0029] Likewise, in some embodiments of the invention the input and
output platforms of the optical switch may be formed from one or
more Photonic Integrated Circuits (PICs). PICs are similar to
planar lightwave circuits, except that whereas planar lightwave
circuits generally only include passive components, photonic
integrated circuits generally also include active optical
integrated devices such as lasers, optical amplifiers, modulators
and the like.
[0030] In some embodiments the input and output platforms shown in
FIGS. 1A and 1B may be monolithically integrated with one another.
In other embodiments, however, the input and output platforms may
be stacked on top of one another hybridly attached using any
suitable technique.
[0031] In some embodiments the input and output waveguides in the
input and output platforms may only support a single polarization
state. In these embodiments polarization diversity may be achieved
by providing a pair of waveguides for each input and output
waveguide, with each waveguide in the pair supporting a different
polarization state. This is shown in FIG. 4 for the input platform
of FIG. 1A. As shown, each input now includes a pair of waveguides
110 and 160. The input to each pair of waveguides 110 and 160
includes a polarization splitter 140 that splits the incoming light
so that a single polarization state is transmitted through each of
the waveguides 110 and 160. A polarization rotator 155 rotates the
polarization state of the light in waveguides 160 so that it has
the same polarization state as the light in waveguides 110. As in
FIG. 1A, waveguides 110 have a series of 1.times.2 optical switches
120 located along it and each of the 1.times.2 optical switches 120
is associated with a vertical coupler 130. Likewise, waveguides 160
have a series of 1.times.2 optical switches 170 located along it
and each of the 1.times.2 optical switches 170 is associated with a
vertical coupler 180. The output platform may be configured in a
manner similar to that shown in FIG. 4 for the input platform to
achieve polarization diversity.
[0032] Numerous advantages arise from the use of a switching
architecture of the type described above. For example, because in
the aforementioned embodiments there are no intervening mode
perturbing structures (e.g., optical elements such as gratings or
taps, waveguide crossings, material or dopant changes,
metallization structures, waveguide dimensional changes, refractive
index profile changes) located along any of the input or output
waveguides between adjacent 1.times.2 switches, waveguide losses at
an given wavelength only depend on or scale with the length of the
waveguides between adjacent 1.times.2 switches. Likewise, optical
losses in a switch conforming to this architecture do not scale
with the number of input or output ports, but only with the overall
physical dimensions of the switch as determined by the total length
of the waveguides.
[0033] Thus, by way of example, optical losses arising in currently
available low loss air clad waveguides may range from about 0.5
dB/cm to 2 dB/cm. Accordingly, for an optical switch employing such
waveguides and having 96 input ports and 96 output ports, and
assuming each waveguide is 5 mm in length, the optical losses
arising in the waveguides will be up to about 0.5 dB. Likewise, for
an optical switch having 1000 input ports and 1000 output ports,
and assuming each waveguide is 50 mm in length, the optical losses
arising in the waveguides will be up to about 5 dB.
[0034] It should be noted that in some embodiments there may be
intervening structures located along one or more of the input
and/or output waveguides, provided that the intervening structure
or structures are actuatable into a state that does not perturb the
mode of the light traveling in the waveguide along which the
intervening structure is located. Any such intervening structure
should give rise to optical losses in the non-perturbing state that
are no greater than that caused by the 1.times.2 optical switches.
For instance, if the 1.times.2 optical switches have a loss in the
through-state of about 0.001 dB, then any intervening structures
should also have loss in their non-perturbing state that is no
greater than, and preferably less than, 0.001 dB.
[0035] In yet other embodiments one or more additional 1.times.2
optical switches of the types mentioned above may be located along
one or more of the input and/or output waveguides. These switches
may be used for purposes other than switching light from an input
port to an output port. For example, these additional 1.times.2
switches may direct light to an optical detector (e.g., a
photodiode) when in their cross states, thereby performing an
optical monitoring function. In one particular embodiment such a
1.times.2 optical switch and optical detector pair may be located
along the input and/or output waveguides between each pair of
adjacent 1.times.2 optical switches that are used to switch light
from the input to the output waveguides. In this way optical
monitoring can be performed at any point along the waveguides after
the light passes traverses any one of the 1.times.2 optical
switches when in the through state.
[0036] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
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